Study On Thermal Distribution For Non-Invasive And Micro-Invasive Thermal Therapy

Hyperthermia is a new study hotspot. Thermal therapy is becoming another important treatment method after surgery, chemical therapy and radio therapy. Many factors would affect treatment result, such as the power, treatment time, properties of tissues, blood perfusion and so on. They need to be considered fully in treatment planning. There are two types: non-invasive and micro-invasive thermal therapy. High intensity focused ultrasound treatment and radiofrequency ablation are typical examples of the two types respectively.For high intensity focused ultrasound treatment, this paper mainly investigated effect of system parameters (especially exposure dose) on thermal field. The simulations explored the relationship of the size and the shape of thermal lesion with the exposure dose determined by sound intensity and exposure time: to achieve a similar thermal lesion, the exposure dose should approximately satisfy the following relation: It0.8=constant. Besides, in situation of scanning model with single-focus, the effect of scanning distance on the temperature field was also studied: while the distance was equal to lesion diameter, the growth rates of highest temperature between two focuses were all above 7% under different heating schemes; with longer scanning distance, effect of the thermal field of former focus on latter focus would be weaker. So during the treatment, we need choose proper scanning distance, and adjust therapeutic parameters while needed. For hepatic radiofrequency ablation, paper used coupled electric-thermal finite element models, and mainly analyzed effect of coolant temperature and blood perfusion on lesion size. Results showed: the hottest part was located about 2-3 mm away from probe surface; and lower coolant temperature created larger lesion. Between 0 and 3.0e-3(1/s) blood perfusion, lesion diameter changed by 33.8%. It showed that blood perfusion influenced temperature and lesion size much. Finally, the paper compared the two ways (50℃isotherm and EM43 thermal dose) to estimate thermal damage.Through the research of high intensity focused ultrasound and hepatic radiofrequency ablation treatment from different aspects, the paper built a set of method which was suitable for thermal distribution of both non-invasive and micro-invasive thermal therapy. The study provided good academic instructional meaning and clinical referenced value for thermal therapy.